1. Field of the Invention
The present invention relates to a Liquid Crystal Display (LCD) device, and more particularly, to a local dimming driving method and device of an LCD device, which is capable of preventing color change due to gray scale saturation when data is compensated while enabling local dimming.
2. Discussion of the Related Art
Recently, as an image display device, a flat panel display device such as a Liquid Crystal Display (LCD) device, a Plasma Display Panel (PDP) device, or an Organic Light Emitting Diode (OLED) device is mainly used.
An LCD device includes a liquid crystal panel for displaying an image using a pixel matrix using electrical and optical characteristics of liquid crystal with anisotropy of a refractive index and a dielectric constant, a driving circuit for driving the liquid crystal panel, and a backlight unit for irradiating light to the liquid crystal panel. Each pixel of the LCD device expresses gray scales, by changing a liquid crystal arrangement direction according to a data signal so as to control transmittance of light from the backlight unit through the liquid crystal panel and a polarization plate.
In the LCD device, the luminance of each pixel is determined by a product of the luminance of the backlight unit and light transmittance of liquid crystal according to data. The LCD device uses a backlight dimming method for analyzing an input image, controlling a dimming value so as to control the luminance of the backlight unit and compensating data, in order to improve a contrast ratio and reduce power consumption. For example, a backlight dimming method decreases the luminance of the backlight unit by decreasing the dimming value and increases the luminance of the backlight unit by compensating data, thereby reducing power consumption of the backlight unit. Most backlight dimming methods allow gray scale saturation, for efficient data compensation. However, when data allowing gray scale saturation is compensated, a color may be changed. That is, the backlight dimming method compensates data by multiplying input data by a gain value detected by the analysis of the input image. However, if the input data includes data allowing gray scale saturation, a color may be changed due to compensation of the data allowing gray scale saturation.
For example, when gray scale saturation is allowed with respect to a gray scale value of data “180” or more, if input R/G/B data “240/200/180” is multiplied by a gain value “1.5” so as to change input R/G/B data to output R/G/B data “255/255/255”, input data close to red is changed to white output data, thereby causing color distortion. If input R/G/B data “100/100/200” is multiplied by a gain value “2” so as to change the input R/G/B data to output R/G/B data “200/200/255”, input data close to blue is changed to output data close to white, thereby causing color distortion.